Indicates if flat button should be displayed.

<div class="definition">
    Boolean, default = false
</div>

Flat button is a small button in the top right corner when sidebar is not in the flat mode and on top when it is. If user clicks
on the flat button <span class="property">onFlat</span> event will be generated.
<div style="height: 10px"></div>

You can define it during object creation:

<textarea class="javascript">
let sidebar = new w2sidebar({
    name: 'sidebar',
    flatButton: true,
    nodes: [
        { id: 'id-1', text: 'Level 1' },
        { id: 'id-2', text: 'Level 2' },
        { id: 'id-3', text: 'Level 3' }
    ]
});
</textarea>

or during run-time:

<textarea class="javascript">
w2ui.sidebar.flatButton = true;
w2ui.sidebar.refresh();
</textarea>